https://bugs.freedesktop.org/show_bug.cgi?id=45968
--- Comment #9 from Tobias Diedrich ranma+freedesktop@tdiedrich.de 2012-02-14 03:00:35 PST --- FWIW using HDMI on 3.3-rc I can go up to 2560x1440@48, but 2560x1440@60 is above the 340MHz pixelclock limit for one link.
I installed XP yesterday and found that it shows the same problem with dual-link not working properly, so this seems to be just a case of bad HW.